1. Field of the Invention
This invention pertains to dewaxing hydrocarbon oils. In particular, it pertains to a method for producing catalytically dewaxed distillate fuel oils with a reduced tendency to form sludge on storage.
2. Prior Art
It is generally known that distillate fuel oils prepared from waxy petroleum crudes will tend to have pour points in excess of 20.degree. F., and that therefore the utility of such distillate fuels is severely limited to environments in which the oil does not lose fluidity. Also, because distillate fuels often are stored for protracted periods of time by both the refiner and the user, it is very desirable that the oil be resistant to the formation of sludge on storage. Good storage stability is particularly important in avoiding excessive maintenance of equipment with oils intended for use as home heating oils or as diesel fuel for the smaller diesel engines.
A process for catalytically dewaxing hydrocarbon oils by selectively cracking the waxy paraffins has recently become known. For example, a process of this nature which employs a mordenite catalyst associated with a hydrogenation component is described in the Oil and Gas Journal, dated Jan. 6, 1975, at pages 69-73. See also U.S. Pat. No. 3,668,113. Another process which utilizes a novel class of synthetic catalysts exemplified by ZSM-5 is described in U.S. Pat. No. Re. 28,398 to Chen et al. This Reissue patent discloses catalytic dewaxing to reduce the pour point not only of distillate oils but also of whole crudes, reduced crudes and syncrudes such as those syncrudes derived from shale. U.S. Pat. No. 3,956,102 and U.S. Pat. No. 4,067,797, both to Chen et al, describe catalytic dewaxing of a distillate oil which has been separated into a low pour point fraction and a high pour point fraction prior to dewaxing, followed by a recombination of the fractions. Of particular interest, as will be more fully explained hereinunder, is the disclosure that although hydrogen gas is used in the catalytic dewaxing step, the dewaxing process described in these last two patents does not consume hydrogen. It is further shown that the wax which is converted produces a light fraction, most of which is in the C.sub.4 to 330.degree. F. boiling range, and very little dry gas. The patents cited above are incorporated herein by reference.
Other patents on catalytic dewaxing also have been issued, including U.S. Pat. Nos. 3,894,938 to Gorring et al; 3,852,189 to Chen et al; 3,968,024 to Gorring; 3,980,550 to Gorring et al; 3,891,540 to Danniel et al; 3,893,906 to Garwood et al; 3,894,931 to Nace et al; 3,894,933 to Owen et al; 3,894,939 to Garwood et al; 3,926,782 to Plank et al; 4,044,064 to Milstein et al; 4,071,574 to Milstein et al; 4,059,648 to Derr et al; and, 4,080,397 to Derr et al. None of the above are believed to disclose or to suggest the present invention.
A method for stabilizing hydrocracked lubricating oils against light instability by treating the oils with olefins and acidic catalysts is described in I&EC PRODUCT RESEARCH & DEVELOPMENT, Volume 17, page 366, December 1978. U.S. Pat. Nos. 3,928,171 and 3,883,416, both to Yan et al, also describe a method for increasing the thermal and light stability and reducing the tendency toward sludge formation in a normally susceptible hydrocarbon oil having a boiling point in excess of 500.degree. F. by treatment with a stabilizing agent in the presence of an acidic catalyst. This publication and patents also are incorporated herein by reference as if fully set forth.
It is an object of this invention to provide an improved process for the manufacture of low pour point distillate fuel oils from waxy crudes. It is a further object of this invention to provide a process for catalytically dewaxing a distillate hydrocarbon oil whereby forming low pour point oils have a reduced tendency to form sludge on storage. These and other objects will become apparent to one skilled in the art on reading this entire specification, including the appended claims.